An object of the present invention is to provide a structural material in the form of a plaster board or the like which is of lower density than generally available yet which has advantageous strength characteristics, particularly with respect to flexure, compression and deflection resistance, and having advantageous sound absorbing and fire resistant properties. A variety of methods have been previously utilized to obtain low density structural material and these efforts have generally been directed toward the formation of cementitious foams and the production of cellular gypsum products. The basis of formation of such materials has generally been the generation or liberation of gases within the cementitious mass by the addition of chemical ingredients reacting in the presence of water. The gas spreads through the mass to form a cellular structure when the cementitious material has set and hardened. Such common gas producing ingredients as aluminum sulfate, alkali carbonates and hydrogen peroxide have been used for this purpose. See for example U.S. Pat. No. Re. 19,506 to Adolph, U.S. Pat. Nos. 2,235,008 to Brownmiller, 2,898,220 to Ulfstedt et al., 2,371,928 to Schneider, 1,946,077 to Kauffmann and 1,620,067 to Brookby et al. Other efforts have been directed toward incorporating a synthetic foaming material such as an organic polymer foam and reference can be made to U.S. Pat. Nos. 2,640,191 to McKee, 2,311,233 to Jaenicke et al. and 2,064,800 to Kauffmann et al. and British Pat. No. 263,571 to Rice. Other references of interest are U.S. Pat. Nos. 3,056,184 to Blaha and 2,676,892 to McLaughlin, Australian Pat. No. 230,162 to Vieli, British Pat. No. 571,284 to Mottershaw and Canadian Pat. No. 521,144 to Sterling. While low density materials have been prepared by methods of some of the foregoing disclosures, they generally lack the strength characteristics required for direct use of such material as wall structures and the like in the building trades. In an effort to overcome these deficiencies it has been suggested to incorporate various fibrous materials in some of the foregoing type of structures. See for example U.S. Pat. Nos. 2,064,800 to Kafuumann et al. (fibrous pulp), 1,808,571 to Raynes (reinforcing strips of heavy paper in cementitious material) and 1,798,609 to Knowlton (reinforcing strips in plaster board). Also of interest are U.S. Pat. No. 1,793,634 to Plunkett (plaster backing sheet incorporating wire mesh) and U.S. Pat. No. 2,664,406 to Armstrong (fissured tile of gypsum cement, amine-aldehyde resin and glass fibers). U.S. Pat. No. 3,062,682 to Morgan et al. is of some interest in disclosing the incorporating of glass fibers in a foamable binder such as a synthetic resin material or a cementitious material.
The present invention provides a reinforced structural material which is of lower density than generally utilized in the building trades but which has high flexure and compression strengths, which resists deflection and has desirable sound absorbing and fire resisting properties. With higher density material (e.g., aluminate) the modulus of rupture can be as high as 300 lbs/in.sup.2 and compression resistance can be as high as 1000 lbs/in.sup.2. The structure consists of polymer modified cementitious foam in which elongate reinforcing members are disposed intimately joined under tension to the structure. The cementitious material sets to form a rigid matrix through which a foamed organic polymer is dispersed. As the plaster sets and the polymer foams, elongate reinforcing members are embedded in the mass and are securely gripped by the rigidifying mass.
In the illustrated embodiment, a mixture of the foaming polymer and cementitious material is advanced to a setting station with the elongate reinforcing member embedded therein fed from a supply, resulting in a tensioning of the reinforcing member and rigid securement in the final slab product. A plurality of the reinforcing members are embedded in the slab spaced along the width dimension of the slab, the elongate members having a greater rigidity in the depth dimension than in the width dimension of the slab. Load testing indicates that the slabs so produced are more polymer foam-like in their flexure properties than plastic-like. The slab can be deflected without cracking over distances greatly in excess of deflections obtainable with plaster board and takes a deflection set in the manner of plastic. Furthermore, the rigid securement of the reinforcing members results in a synergistic increase in deflection resistance, values being obtained which are greatly in excess of the sum of deflection values obtained for the slab without reinforcement and for the reinforcement members. The cellular matrix configuration of the slab structure provides sound absorbing and fire and heat resisting properties superior to the structures in general building use.